Turbine systems are known in the art and used to convert energy from a fluid flow into useful work. The simplest turbine system has one moving part, a rotor assembly, which conventionally takes the form of a shaft or drum with blades attached thereto. In operation, the moving fluid typically acts on the blades so as to produce rotation of the rotor. Exemplary turbine systems include windmills, watermills, as well as gas and steam turbines.
It is generally accepted in the art that the kinetic energy of wind is a function of the wind velocity, mass and cross-sectional area traversed by the wind. For example, one goal in the design of a windmill is to ensure that the mill can continue to operate at low wind speeds. To date this has been accomplished by use of lighter materials as well as by improving the structure and operation of the blades, and the manner in which the blades react to the flow of the wind. It is conventionally known in the art to use one or more wheels in connection with a windmill. The wheels are generally capable of rotation and adapted to capture the wind. In one design, two wheels can be mounted co-axially and adapted for oppositely rotation. However, the prior art has, thus far, failed to fully address several known drawbacks.
For example, U.S. Pat. No. 4,061,926 to Peed dated Dec. 6, 1977 teaches an electric generating system in which oppositely rotating wind driven wheels are used, one to drive the rotor and one to drive the stator of an electric generator. The system comprises two wind driven turbines having radially extending vanes mounted coaxially one above the other on a tubular stationary post-like support. However, the conventional device appears to use an additional mechanical synchronizer which is interposed between the two wheel structures so as to ensure that the two wheels rotate at the same speed, in variable wind conditions. The additional synchronizer, thus, adds to the overall complexity of the system and does not fully address the problem of operating the turbine when the wind speed is low or very low.
U.S. Pat. No. 4,074,951 to Hudson dated Feb. 21, 1978 describes a wind power converter including, inter alia, a pair of rotatable turbines with elongated curved blades disposed within a rotatable housing on axially parallel shafts. The conventional device also includes means for synchronizing the rotation of the turbines, and further includes fluid pumping means which must be connected to the turbine shafts.
U.S. Pat. No. 5,855,470 to Holmes dated Jan. 5, 1999 describes a wind wheel having at least one planetary gear wheel affixed rigidly to a wind-wheel axle from which gear trains for each of a plurality of wind-wheel plates are rotated to maximum plate frontage in wind flow by gear belts intermediate the gear trains and axes of the plurality of wind-wheel plates. The wind wheel can be structured with either a horizontal axis or a vertical axis with appropriate structural modifications. Directional control can be provided by eccentric positioning of the wind-wheel axis in order for the wind-wheel plates to have a weather-vane effect.
U.S. Pat. No. 6,688,925 to Garcia dated Feb. 10, 2004 describes two supporting wheels mounted permanently on a main shaft. Between those two wheels are four blades, or sails, that will transfer the power of wind and running water to the main shaft to make it rotate.
U.S. Pat. No. 7,323,791 to Jonsson dated Jan. 29, 2008 describes a wind turbine with a plurality of moveable members configured to direct air flow onto a first half of the rotatable frame and to block air flow onto a second half of the rotatable frame to thereby cause the rotatable frame to rotate. The moveable members may be pivotable louvers that can be opened by being oriented in a direction parallel to the direction of the air flow.
International Publication No. WO/2011/115845 dated Sep. 22, 2011 describes a wind turbine including a plurality of coaxial, counter-rotating turbine assemblies. First and second shroud assemblies define a generally spherical volume containing the first and second turbine assemblies. The first and second shroud assemblies each include a shroud member that can selectively shield or expose portions of the respective turbine assemblies to the wind by changing the rotational position of the shroud members about the system axis. The turbine assemblies are interconnected to a generator for the production of electrical power.
What is needed, therefore, is a wind turbine that is capable of operating in variable wind conditions, including high velocity or low velocity wind. Such a wind turbine should be easy to operate, while being relatively inexpensive to build and maintain.